1. Field of the Invention
The invention relates to a display apparatus and a display method in which video signals of a plurality of systems can be individually or simultaneously properly displayed to one CRT.
2. Description of the Related Art
In a video signal which is displayed on a television monitor or the like, a plurality of video systems having different video signal formats exist. As is well known, in a video signal by the television broadcasting, for example, in the NTSC system used in Japan, a system such that the signal is transmitted mainly as a radio wave and an interlace scan is performed at a ratio of 525 lines/59.94 Hz is used. In the HDTV broadcasting for the purpose of obtaining a video image of high resolution, a system of the interlace of 1125 lines/60 Hz is used. In a personal computer, the scan is performed in a non-interlace manner and what is called a multi-scan corresponding to a plurality of kinds of vertical frequencies and horizontal frequencies is generally used and a plurality of kinds of resolutions can be selected as resolutions of a video monitor.
In recent years, in association with the progress of the techniques regarding a home-use television receiver, a monitor for a personal computer, and the like, a display apparatus which can display both of the video signal by the television broadcasting and the video signal that is outputted from the personal computer has been proposed. In such a display apparatus, a system for displaying a video image by using a CRT (Cathode Ray Tube) is a main stream.
It is known that such a kind of display apparatus is realized by combining a construction of multi-scan of the horizontal deflection and vertical deflection in order to display the video signal by the personal computer to a construction of a conventional television receiver such as a tuner which can properly receive a radio wave of the television broadcasting of the NTSC system or HDTV system or a decoder (including a color decoder) for demodulating the received video signal and audio signal.
If the above requirements are merely provided, a sufficient display quality cannot be obtained in the CRT. For instance, when a video image by the television broadcasting is monitored, unless a sufficient luminance of the video image is derived, powerfulness is missing. On the other hand, usually, since the video signal by the personal computer has higher resolution and higher precision as compared with those of the video image by the television broadcasting, importance is paid to the focusing characteristics rather than the luminance.
In the conventional CRT monitor, by changing a driving voltage of the CRT in accordance with the kind of signal to be displayed, one CRT is made to correspond to those different video signals, thereby realizing high luminance of the video signal. That is, when the video image by the television broadcasting is displayed, the driving voltage is stepped up, thereby obtaining the video image of high luminance. When the video image by the personal computer is displayed, the driving voltage is stepped down.
However, according to the above method, in a driving voltage generating circuit, a dynamic range of an output voltage is enlarged in association with the step-up of the driving voltage. There is, consequently, a problem such that the costs of the driving voltage generating circuit are raised.
There is also a problem that unnecessary radiation from the CRT and peripheral circuits increases due to the step-up of the driving voltage.
It is, therefore, an object of the invention to provide a display apparatus and a display method which can display video signals of a plurality of kinds of formats by one CRT at proper luminance and resolution without changing a driving voltage.
To solve the foregoing problems, according to the invention, there is provided a display apparatus for displaying video signals of two or more different formats by one CRT, comprising: bias voltage output means for outputting a bias voltage to said CRT; and voltage switching means for switching said bias voltage which is outputted from said bias voltage output means in accordance with the video signal which is supplied to said CRT.
To solve the foregoing problems, according to the invention, there is provided a display method for displaying video signals having two or more different formats by one CRT, comprising the steps of: detecting a kind of the video signal; and switching a bias voltage to said CRT in accordance with the detected kind of said video signal.
To solve the foregoing problems, according to the invention, there is provided a display apparatus for displaying a single video signal by one CRT, comprising: bias voltage output means for outputting a bias voltage to said CRT; and voltage switching means for switching said bias voltage which is outputted from said bias voltage output means for a predetermined period of time.
As mentioned above, according to the invention, since the bias voltage to the CRT is switched in accordance with the video signal which is supplied to the CRT, the luminance and resolution of the CRT can be changed without changing a driving voltage.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.